Simulation-based mastery learning (SBML) decreases serious iatrogenic complications from central venous catheter insertion. Given medical procedures are the second most common cause of the complications that afflict 3% of hospitalized patients, SBML should be applied to procedures done in all medical centers. In academic hospitals, bedside procedures such as thoracentesis (removal of fluid in the chest) are often performed by unsupervised medical trainees. Traditionally, medical trainees learn procedures relying on the historic see one, do one, teach one mentality. Unfortunately, this approach subjects patients to procedures before trainees are competent. Through the use of medical simulation, medical educators can increase the essential knowledge and skills of trainees while assuring procedural competence and reducing patient exposure to undue risk. Medical simulation training using the mastery learning model improves clinical skills and reduces the risk of procedure- associated injury. Our research group pioneered the use of this evidence-based approach for teaching medical trainees. Mastery learning requires that all trainees demonstrate a uniformly high level of skill before training completion. This ensures competence on a medical simulator before actual patient encounters. The goal of the proposed research is to investigate the use of an SBML curriculum to improve internal medicine residents' skills when performing thoracenteses on patients. Additionally, we will evaluate how these skills affect patient outcomes by comparing thoracenteses performed by simulator-trained residents to those who have traditional training. This project will evaluate these overall hypotheses: 1) simulation-based training using the mastery learning approach improves thoracentesis skills and knowledge; 2) this methodology will promote retention of the learned skills, and; 3) result in improved patient outcomes, reduced length of stay, and medical costs. Specific aims are: 1) redesign a thoracentesis procedure curriculum, based on the mastery learning model, using simulators, ultrasound, and web-based didactic instruction to train medical residents; 2) measure changes in medical resident skills as they undergo the curriculum, 3) assess the stability of trainees' thoracentesis procedure skills over a one year period following formal simulation training with mastery learning, and; 4) demonstrate whether using the mastery learning procedure curriculum compared to a traditional learning approach decreases iatrogenic complications from thoracentesis and improves healthcare utilization through reductions in length of hospital stay and decreased cost. The proposed study will demonstrate that SBML significantly decreases iatrogenic complications and healthcare costs from thoracenteses performed by physicians in training. Results from this study may inform policy to require formal competency-based training using simulation technology for all bedside procedures.